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205 lines
13 KiB
XML
205 lines
13 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glBeginQuery">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>2005</year>
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<holder>Sams Publishing</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>glBeginQuery</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glBeginQuery</refname>
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<refpurpose>delimit the boundaries of a query object</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glBeginQuery</function></funcdef>
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<paramdef>GLenum <parameter>target</parameter></paramdef>
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<paramdef>GLuint <parameter>id</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<!-- eqn: ignoring delim $$ -->
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>target</parameter></term>
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<listitem>
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<para>
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Specifies the target type of query object established between
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<function>glBeginQuery</function> and the subsequent <citerefentry><refentrytitle>glEndQuery</refentrytitle></citerefentry>.
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The symbolic constant must be one of <constant>GL_SAMPLES_PASSED</constant>, <constant>GL_ANY_SAMPLES_PASSED</constant>,
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<constant>GL_PRIMITIVES_GENERATED</constant>, <constant>GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN</constant>, or
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<constant>GL_TIME_ELAPSED</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>id</parameter></term>
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<listitem>
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<para>
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Specifies the name of a query object.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glEndQuery</function></funcdef>
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<paramdef>GLenum <parameter>target</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<!-- eqn: ignoring delim $$ -->
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<refsect1 id="parameters2"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>target</parameter></term>
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<listitem>
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<para>
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Specifies the target type of query object to be concluded.
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The symbolic constant must be one of <constant>GL_SAMPLES_PASSED</constant>, <constant>GL_ANY_SAMPLES_PASSED</constant>,
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<constant>GL_PRIMITIVES_GENERATED</constant>, <constant>GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN</constant>, or
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<constant>GL_TIME_ELAPSED</constant>.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para>
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<function>glBeginQuery</function> and <citerefentry><refentrytitle>glEndQuery</refentrytitle></citerefentry> delimit the
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boundaries of a query object. <parameter>query</parameter> must be a name previously returned from a call to
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<citerefentry><refentrytitle>glGenQueries</refentrytitle></citerefentry>. If a query object with name <parameter>id</parameter>
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does not yet exist it is created with the type determined by <parameter>target</parameter>. <parameter>target</parameter> must
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be one of <constant>GL_SAMPLES_PASSED</constant>, <constant>GL_ANY_SAMPLES_PASSED</constant>, <constant>GL_PRIMITIVES_GENERATED</constant>,
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<constant>GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN</constant>, or <constant>GL_TIME_ELAPSED</constant>. The behavior of the query
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object depends on its type and is as follows.
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</para>
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<para>
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If <parameter>target</parameter> is <constant>GL_SAMPLES_PASSED</constant>, <parameter>target</parameter> must be an unused name,
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or the name of an existing occlusion query object.
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When <function>glBeginQuery</function> is executed, the query object's samples-passed counter is reset to 0. Subsequent
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rendering will increment the counter for every sample that passes the depth test. If the value of <constant>GL_SAMPLE_BUFFERS</constant>
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is 0, then the samples-passed count is incremented by 1 for each fragment. If the value of <constant>GL_SAMPLE_BUFFERS</constant>
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is 1, then the samples-passed count is incremented by the number of samples whose coverage bit is set. However, implementations, at their
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discression may instead increase the samples-passed count by the value of <constant>GL_SAMPLES</constant> if any sample in the fragment
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is covered. When <function>glEndQuery</function>
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is executed, the samples-passed counter is assigned to the query object's result value. This value can be queried by
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calling <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry> with <parameter>pname</parameter>
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<constant>GL_QUERY_RESULT</constant>.
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</para>
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<para>
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If <parameter>target</parameter> is <constant>GL_ANY_SAMPLES_PASSED</constant>, <parameter>target</parameter> must be an unused name,
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or the name of an existing boolean occlusion query object.
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When <function>glBeginQuery</function> is executed, the query object's samples-passed flag is reset to <constant>GL_FALSE</constant>.
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Subsequent rendering causes the flag to be set to <constant>GL_TRUE</constant> if any sample passes the depth test. When
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<function>glEndQuery</function> is executed, the samples-passed flag is assigned to the query object's result value. This value can
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be queried by calling <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry> with <parameter>pname</parameter>
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<constant>GL_QUERY_RESULT</constant>.
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</para>
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<para>
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If <parameter>target</parameter> is <constant>GL_PRIMITIVES_GENERATED</constant>, <parameter>target</parameter> must be an unused
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name, or the name of an existing primitive query object previously bound to the <constant>GL_PRIMITIVES_GENERATED</constant> query binding.
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When <function>glBeginQuery</function> is executed, the query object's primitives-generated counter is reset to 0. Subsequent
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rendering will increment the counter once for every vertex that is emitted from the geometry shader, or from the vertex shader if
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no geometry shader is present. When <function>glEndQuery</function> is executed, the primitives-generated counter is assigned to
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the query object's result value. This value can be queried by calling <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry> with <parameter>pname</parameter>
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<constant>GL_QUERY_RESULT</constant>.
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</para>
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<para>
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If <parameter>target</parameter> is <constant>GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN</constant>, <parameter>target</parameter> must be
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an unused name, or the name of an existing primitive query object previously bound to the <constant>GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN</constant>
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query binding. When <function>glBeginQuery</function> is executed, the query object's primitives-written counter is reset to 0. Subsequent
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rendering will increment the counter once for every vertex that is written into the bound transform feedback buffer(s). If transform feedback
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mode is not activated between the call to <function>glBeginQuery</function> and <function>glEndQuery</function>, the counter will not be
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incremented. When <function>glEndQuery</function> is executed, the primitives-written counter is assigned to
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the query object's result value. This value can be queried by calling <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry> with <parameter>pname</parameter>
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<constant>GL_QUERY_RESULT</constant>.
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</para>
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<para>
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If <parameter>target</parameter> is <constant>GL_TIME_ELAPSED</constant>, <parameter>target</parameter> must be
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an unused name, or the name of an existing timer query object previously bound to the <constant>GL_TIME_ELAPSED</constant>
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query binding. When <function>glBeginQuery</function> is executed, the query object's time counter is reset to 0. When <function>glEndQuery</function>
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is executed, the elapsed server time that has passed since the call to <function>glBeginQuery</function> is written into the query object's
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time counter. This value can be queried by calling <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry> with <parameter>pname</parameter>
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<constant>GL_QUERY_RESULT</constant>.
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</para>
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<para>
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Querying the <constant>GL_QUERY_RESULT</constant> implicitly flushes the GL pipeline until the rendering delimited by the
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query object has completed and the result is available. <constant>GL_QUERY_RESULT_AVAILABLE</constant> can be queried to
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determine if the result is immediately available or if the rendering is not yet complete.
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</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para>
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If the query target's count exceeds the maximum value representable in the number of available bits, as reported by
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<citerefentry><refentrytitle>glGetQueryiv</refentrytitle></citerefentry> with <parameter>target</parameter> set to the
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appropriate query target and <parameter>pname</parameter>
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<constant>GL_QUERY_COUNTER_BITS</constant>, the count becomes undefined.
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</para>
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<para>
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An implementation may support 0 bits in its counter, in which case query results are always undefined
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and essentially useless.
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</para>
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<para>
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When <constant>GL_SAMPLE_BUFFERS</constant> is 0, the samples-passed counter of an occlusion query will increment once for each
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fragment that passes the depth test. When <constant>GL_SAMPLE_BUFFERS</constant> is 1, an implementation may either increment
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the samples-passed counter individually for each sample of a fragment that passes the depth test, or it may choose to increment
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the counter for all samples of a fragment if any one of them passes the depth test.
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</para>
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<para>
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The query targets <constant>GL_ANY_SAMPLES_PASSED</constant>, and <constant>GL_TIME_ELAPSED</constant> are availale only if
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the GL version is 3.3 or higher.
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</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>target</parameter> is not one of the accepted tokens.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glBeginQuery</function> is executed while
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a query object of the same <parameter>target</parameter> is already active.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <citerefentry><refentrytitle>glEndQuery</refentrytitle></citerefentry>
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is executed when a query object of the same <parameter>target</parameter> is not active.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>id</parameter> is 0.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>id</parameter> is the name of an already active query object.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>id</parameter> refers to an existing query object whose type
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does not does not match <parameter>target</parameter>.
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</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glDeleteQueries</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glGenQueries</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glGetQueryiv</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glIsQuery</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 2005 Addison-Wesley.
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This material may be distributed subject to the terms and conditions set forth in
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the Open Publication License, v 1.0, 8 June 1999.
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<ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
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</para>
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</refsect1>
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</refentry>
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